The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ANR automatic neighbor relations
BSIC base transceiver station identity code
CPICH common pilot channel
DCH dedicated (physical) channel
DL downlink (node B towards UE)
EUTRAN evolved UTRAN (LTE)
LTE long term evolution
NCL neighbor cell list
Node B base station
RRC radio resource control
RSCP received signal code power
SI system information
SON self optimizing network
TDD time division duplex
UE user equipment
UL uplink (UE towards node B)
UTRAN universal terrestrial radio access network
For handover and reselection of mobile terminals/UEs from one cell/base station to another some wireless systems have the UE maintain a list of neighbor cells which the UE measures the signal power it receives. Reporting on this RSCP to the serving cell allows the network to more intelligently choose when and to which cell to handover the UE.
But the UE is mobile and so has a limited power supply. The idle mode is intended to conserve the UE's power supply but still the idle mode UE takes measurements of neighbor cells in order to facilitate handovers since the idle UE may still be moving and need handover. In some radio technologies such as UTRAN, for example to facilitate operators to minimize drive tests, the idle UE takes its neighbor cell measurements and stores them temporarily, then reports it's collected and logged measurement data en masse to the network at some predetermined time which is somewhat later than when the earliest logged measurements were taken. This allows the UE to avoid exiting the idle mode simply to report neighbor cell identities and signal strengths.
A problem arises in that the neighbor cell list NCL which the UE uses for this purpose may not be up-to-date for the current geographic location of the UE. The UE receives its NCL from its serving cell but assuming mobility of the idle UE there may be neighbor cells in the UE's locally stored NCL which are no longer viable neighbors, and there may also be viable neighbor cells which are not in the UE's NCL. The latter situation, which may arise for example due to pico/micro cells (e.g., open or closed subscriber group cells) within a neighbor macro cell may be handled in one of two ways. The UE may simply ignore cells which are not in its NCL, but this may lead to improper handovers and reselections to the wrong cell and/or at the wrong time. Alternatively, the UE may detect and take measurements on those cells not in its NCL whose RSCP is sufficiently strong and report them leaving analysis of the most appropriate handover cell candidate to the network which is not power constrained.
The trend in ongoing development of UTRAN systems (e.g., 3GPP TSG-RAN WG2 meeting #72) is to report cells which are not within the NCL, which for brevity is termed logged ANR in 3GPP. See for example document R2-106257 entitled DISCUSSION ON UMTS ANR NON CELL_DCH BASED APPROACH (LOG APPROACH) by Huawei and HiSilicon; document R2-106442 entitled METHOD FOR ANR SUPPORT IN UTRAN by Ericsson and ST Ericsson; and document R2-106625 entitled CONFIGURATION AND REPORTING FOR MDT BASED ANR by Samsung (all at 3GPP TSG-RAN WG2 #72; Jacksonville, USA; 15-19 Nov. 2010). Certain aspects of these proposals extend concepts employed for minimum drive time MDT measurements, by which selected UEs take periodic measurements which are reported to the network at some later UE transmit opportunity and which the network uses for routine network analysis and optimization, distinct from directly managing the reporting UE.
Considering the limited power of mobile terminals, measuring cells not in a UE's NCL raises certain problems. Specifically, if a UE is to report cells other than those in its NCL, it must also identify in its measurement report the cell global identity from which the non-NCL measurements were taken. Most cell global identifiers IDs are readily available from system information SI broadcast by the cell itself, but to get this cell ID the UE would have to decode SI of the non-NCL cells, a task not necessary for mere signal strength measurements.
Over an extended period of idle time this could be performed repeatedly which would result in a non-negligible drain on UE power reserves, reducing the maximum idle/standby time which many users consider as part of their mobile phone purchasing decision. Over a shorter period of time it is reasonable that radio channel conditions might be changing to an extent that some macro neighbor cells are detected which are not in the UE's NCL. Highly dynamic radio channel conditions might also cause the RSCP seen by the same UE for the same cell to move over and under the signal strength threshold for taking a measurement, effectively appearing and disappearing from the UE's measurement ‘view’. In this case potentially the UE would have to decode the same SI from the same cell each time the UE's RSCP for that cell went over the threshold and make duplicate log entries, for only after decoding SI for each time RSCP exceeds the threshold will the UE know that the cell has the same global identity as one previously logged.
Various exemplary embodiments detailed below address the above problems to various extents.